Mirena IUS - A Different Type of Coil
Mirena IUS is like many other types of Intrauterine Contraceptive
Devices (IUCD's) in that it is fitted by a doctor and remains in the
womb for a fixed amount of time, after which it must be changed. It is
different, however, in that it is much more effective than usual IUCD's
and avoids many of the side effects that put women off this choice of
In this article the abbreviation IUCD refers to this whole group of
contraceptives, and the terms Mirena and IUS will be used
Most IUCD's make a woman's periods heavier, but the Mirena makes
periods lighter than usual. Because of this, it is frequently used as a
treatment for heavy periods, even in women who don't need
contraception. As can be seen in the picture, it is made of a light,
plastic, T-shaped frame with the stem of the 'T' a bit thicker than the
rest. This stem contains a tiny storage system of a hormone called
Levonorgestrel. This hormone is also used in contraceptive pills such
as Eugynon, Logynon, Microgynon, Ovran 30, Ovranette and Trinordial. In
the Mirena, however, a much lower dose is released than when you take
the Pill (about 1/7th strength), and it goes directly to the lining of
the womb, rather than through the blood stream where it may lead to the
common progesterone-type side effects (see below).
How Effective is the Contraception?
If 1000 women used the Mirena IUS for a year, only one would fall
pregnant. This compares with about 10 for the normal IUCD, 20 for the
Pill and 10-15 for the injection (Depo Provera). This is comparable to
the effectiveness of sterilisation
Mirena acts as a contraceptive in two ways: it makes the mucus at
the neck of the womb (the cervix) much thicker, preventing sperm from
getting through and it also makes the lining of the womb extremely
thin, stopping implantation. In some women it prevents egg release
As with all IUCD's, if it does fail, there is a higher risk of ectopic
pregnancy (a pregnancy located outside the womb, usually in the tube).
If you felt pregnant or had a positive pregnancy test, it is important
to see your doctor to rule this out. Overall, however, compared to
women not using any contraception, the risk of ectopic pregnancy is
greatly reduced (around 2 per 10,000 women each year because the IUS is
such a good contraceptive.
If a pregnancy does occur with an IUCD, it is advisable to remove the
contraceptive if possible - this reduces the risk of bleeding,
infection and miscarriage. Because failure is so rare, there is little
information available on the effects on an ongoing pregnancy with the
Mirena still in place.
Fitting the Mirena IUS
Before it is inserted, the doctor will do an examination to make sure
the womb is a normal size and there is nothing else unusual to find. If
there is some discharge, swabs will be taken to rule out infection
before it is placed. The IUS is inserted within a week of beginning a
period - this helps to reduce the chance of expulsion and irregular
bleeding (as the womb lining is already quite thin at this time). It
may be inserted immediately after surgical termination of pregnancy,
but should be deferred until 6 weeks after delivery of a baby.
A speculum is placed in the vagina, like when you have a normal
smear test, and the Mirena is placed into the womb through the cervix.
Because it contains the storage of hormone, the stem is slightly wider
than in normal IUCD's. This can occasionally lead to difficulties with
fitting, especially if you have not had a baby before. In this
situation, it would be helpful to use some local anaesthetic. It should
be fitted by someone who has been trained and has experience in fitting
It is a good idea to take some painkillers a couple of hours before
the fitting - this will help reduce any discomfort. A good choice is
Ibuprofen 400 mg, which can be bought over-the-counter at a chemist
(please check that this is safe for you). Most women do not find the
insertion procedure very uncomfortable - usually much less than
Once the IUS is in place, you won't be able to 'feel' it in your womb.
Your doctor will show you how to check for the strings, and it is very
unusual for your partner to be aware of it during intercourse. After
fitting, a further appointment should be made for six weeks later to
check the strings can still be seen. Yearly checks are advised after
Removing or Changing the Mirena
Removal involves a speculum examination again and the IUS is removed by
pulling on the strings. This is only uncomfortable for a second or two
as it comes out. The hormone effect on the lining of the womb is
reversed within a month and normal periods and fertility returns.
The IUS will last 5 years and, if required, a new one can be inserted at the same time the old one is removed.
Mirena for Heavy Periods
Although the IUS was originally developed as a contraceptive,
the discovery that it leads to much lighter periods was a great bonus.
Many gynaecologists now suggest the Mirena as a treatment for heavy
periods if tablet treatment doesn't work.
After 3 months use, the average blood loss is 85% less, and by 12
months the flow is reduced by 97% every cycle. About one third of women
using the IUS will not have any periods at all. Although women
initially find it a bit unusual not having periods, it doesn't cause
any problems. There is no 'build up' of blood, because the hormone in
the IUS prevents the lining of the womb from building up at all. Often
it is the excessive thickening of this lining that is the cause of the
problems in the first place.
One study looked at 54 women who had heavy periods and were awaiting
hysterectomy. They all used the Mirena, and just under 70% were taken
off the waiting list because they were happy with the treatment. In
another study of 50 similar women, 82% avoided major surgery.
The Mirena is now licensed for treating heavy periods, and although
this official licensing is relatively new, it has been used
'off-license' for some time in this way.
Although the IUS isn't primarily used for painful periods, two
studies have found that it does help in many cases (as often as 80% of
the time). If painful periods persist, it is usual to rule out any
other problems with a laparoscopy.
Large fibroids are a common cause of heavy periods. If they are so
large, or in such a position that they make the inside of the womb an
abnormal shape, it is unlikely that the Mirena will remain in place,
and would not be helpful as a treatment. With small to moderate size
fibroids, it is quite reasonable to use the IUS and one study has found
that fibroids are less common in women who use the Mirena. A further
paper has found that in the 5 women studied, a Mirena actually reduced
the size of their fibroids. This is only one report, of course, and the
IUS cannot be recommended as a treatment for fibroids based on this
alone, though it is very interesting.
Premenstrual Syndrome (PMS)
PMS is a syndrome that is thought to be caused by the varying hormones
of the menstrual cycle. There have been suggestions that the IUS may be
useful as it will allow a continuous dose of hormones to be given
(oestrogen) without the worry of excessive stimulation of the lining of
the womb. Usually oestrogens are combined with a course of a
progestagen to prevent this, but many women experience PMS-like
symptoms with progestagens. At present there is little published in the
medical literature about the use of the Mirena in this way, but for
severe cases, where hysterectomy is being considered as the only
remaining alternative, it would certainly be reasonable to consider
Hormone Replacement Therapy (HRT)
There is a growing experience with the use of the IUS for women who
require hormone replacement therapy see
www.epigee.org/menopause/hrt.html, but who have either bad PMS-like
symptoms or erratic bleeding on normal HRT preparations. The IUS with
continuous implants, tablets or patches of oestrogen provides good
symptom relief with minimal side effects. As its use in this way is not
generally established in the UK, this would normally be prescribed
under the care of a gynaecologist. In other countries (eg. Finland) the
IUS is licensed for use in this way and can be routinely used for up to
Women who have experienced an ectopic pregnancy are at a greater
risk of this happening again in future pregnancies. For this reason,
they are advised to choose a type of contraception that does not
increase this risk any further - in particular they are encouraged to
avoid IUCD's, as these are known to increase this risk. The risk of
ectopic pregnancy is very much lower with the IUS than in women not
using any contraception (60 times lower, in fact). Although perhaps not
a first choice, the IUS may be considered when other contraceptives are
really not suitable. As with most decisions in medicine, it is about
the balance of risk.
Expulsion: In the early months of use,
there is a very small chance that the IUS may dislodge and come out,
either in part or altogether. This risk may be greater than with other
IUCD's, presumably because it is that bit larger. There may be symptoms
such as bleeding or persistent pain not relieved by simple pain
killers, or it might be passed without any discomfort at all. As the
system reduces blood flow, sudden return of heavy periods might suggest
this has happened.
Hormonal Problems: Although the IUS
delivers its hormone directly to the lining of the womb, it does lead
to a slight increase in progesterone levels in the blood stream. The
levels are much lower than that found with the progestagen-only pill
(POP) and usually don't lead to side effects. If they do occur, most
often they are mild and only last up to 4-6 weeks. Side effects have
included headache, water retention, breast tenderness or acne.
Ovarian Cysts: Progestagen hormones
increase the chance of benign, simple ovarian cysts. This is more
common with the higher hormone levels associated with the
progestagen-only pill. Overall the risk is about 3 times higher (1.2%
in IUS users versus 0.4% normally). These cysts most often do not
require any treatment and resolve on their own over 2-3 months. It is
usual to arrange follow-up ultrasound scans over this time if they do
occur. The most common symptoms of a cyst is abdominal pain that
doesn't settle with simple painkillers.
Bleeding Problems: These are without a
doubt the most common problem associated with the Mirena. It takes
about 3 months for the lining of the womb to thin down and during this
time bleeding can be erratic or even heavy at times, but almost always
settles after 3-6 months. During the first month, 20% of users
experience prolonged bleeding of more than 8 days duration, but by the
third month only 3% have prolonged bleeding.
Pelvic Infection: In general IUCD's
increase the risk of infection of the womb, tubes and other pelvic
organs. Studies looking at Mirena suggest that this may not be the
case, with the IUS being protective against infection, particularly in
the age group most at risk (<25y). Although this would fit with the
thickening of the cervical mucus preventing infection getting through
the cervix, this finding is not universal in all studies. The actual
long-term risk of infection is very low, at less than 1% with 5 years'
use. A World Health Organisation study of over 22,000 users found that
the infection risk was only increased in the first 20 days after
insertion. This demonstrates the need to rule out infection in
high-risk women before inserting the IUS, and in this group a Chlamydia
screen is advised.
The IUS is an effective contraceptive and treatment for heavy periods.
It reduces menstrual pain, may be used with small to moderate fibroids
and has the potential as a treatment for severe PMS. It is associated
with a low risk of ectopic pregnancy and infection. It may be more
difficult to insert than standard IUCD's, in some women can lead to
mild hormonal effects, and commonly causes irregular bleeding in the
initial months, though this usually settles by 3-6 months. It is a
particularly good treatment choice for women with heavy periods who
wish to avoid major surgery.